Optical readout device

ABSTRACT

An optical readout device for reading out data from an electroluminescent data storage medium, comprising: a driving circuit ( 4 ) for driving the radiation-emitting material with a time-varying applied signal; a radiation detector array ( 6 ) for detecting radiation emitted from the data storage medium and for generating radiation detection signals; and a processing part ( 8 ) arranged to process the detection signals to distinguish a detection signal resulting from reading different types of marks in the data storage medium in dependence on a timing reference signal.

This invention relates to an optical readout device, in particular to anoptical readout device for reading out data from a data storage mediumcomprising a radiation-emitting material which radiates under theinfluence of an applied signal. Various phenomena are known wherebymaterials emit radiation under the influence of an applied signal. Oneexample is electroluminescence whereby materials emit radiation underthe influence of an applied voltage signal. Another is fluorescencewhereby materials emit radiation under the influence of an excitingradiation signal.

International patent publication no. WO-A-0048197 describes anelectroluminescent multi-layer optical information storage medium whichhas multiple information layers. On each layer, information is stored inthe form of an electroluminescent material. The information is organizedinto regions called pages. A specific page on a specific layer can beaddressed through electrodes integrated into the medium. Data is codedinto the medium in the form of electroluminescent characteristics, whichvary in accordance with a data value being read out.

It would be desirable to increase the data density in data storagesystems using data recording mediums capable of emitting radiation underan applied signal.

In accordance with the present invention there is provided an opticalreadout device for reading out data from a radiation-emitting datastorage medium, said medium comprising a radiation-emitting materialholding data in the form of data storage areas capable of emittingvarying amounts of radiation on application of an applied signal, saiddata storage areas including at least a first type of data storage areaand a second type of data storage area indicating different first andsecond data values, said device comprising:

-   -   a driving part for driving the radiation-emitting material with        an applied signal;    -   a radiation detecting part for detecting radiation emitted from        said data storage areas and for generating radiation detection        signals; and    -   a processing part for processing said detection signals to        generate data signals corresponding to the data stored in the        medium;    -   wherein said driving part is arranged to generate a time-varying        applied signal, and wherein the processing part is arranged to        process the detection signals to distinguish a detection signal        resulting from reading said first type of data storage area from        a detection signal resulting from reading said second type of        data storage area in dependence on a temporal characteristic of        the detection signals.

The invention provides an effective means for the read out of data froma data storage medium storing data in the form of areas having differentlevels of emissivity.

In a preferred embodiment, the invention implements a multi-level datacoding scheme, in which at least three different levels of emissivityare encoded into the data storage medium. In implementing such amulti-level coding scheme, one method would be to use a detector arrayproducing analogue signals, and to provide an analogue-to-digitalconverter for each of the different detectors to produce anappropriately digitized level and hence retrieve the stored information.However, this would involve complex electronic circuitry for eachdetector, or alternatively reduce data-extraction speeds for the arrayas a whole. The use of the present invention allows, as a minimum, asingle digital-to-analogue converter, or a single analogue-to-digitalconverter, to be used, thereby significantly reducing the complexity ofthe device.

A further advantage is that the scanning speed can be adjusted to adaptthe device to different signal-to-noise ratios in the system, or thenumber of levels chosen in the multi-level coding scheme.

Further features and advantages of the invention will become apparentfrom the following description of preferred embodiments of theinvention, given by way of example only and made with reference to theaccompanying drawings, wherein:

FIG. 1 is a schematic illustration of an optical read out device inaccordance with an embodiment of the invention;

FIG. 2 is a graph showing relationships between drive voltage andbrightness for an electroluminescent material;

FIG. 3 is a schematic illustration showing further details of thearrangements shown in FIG. 1; and

FIG. 4(A) to (C) are graphs showing detection signals from a detector inaccordance with an embodiment of the invention.

Referring now to FIG. 1, the invention relates to an optical read outdevice for reading out data from a radiation-emitting data storagemedium 2. In one embodiment, the data storage medium 2 is an organiclight emitting device (OLED) containing a planar layer of organicelectroluminescent material, such as polyphenylene-vinylene (PPV)sandwiched between two planar electrode layers, at least the upper ofwhich is formed of a transparent conductive material, such as indium tinoxide (ITO). Data is stored by locally modifying the strength ofemission of the material in discrete data storage areas of the material.The strength of emission of the data storage areas is varied betweendata storage areas. Such variation can be achieved either bypre-patterning lithographically during the manufacture of the datastorage medium, in which case the medium is of a read-only type, or byusing a writing device, which may be combined with the read-out deviceof the present invention, including radiation light source, such as alaser beam or an ultraviolet light beam, to reduce the strength ofemission in data areas selectively during a writing process, in whichcase the medium is of a singularly writable or multiply re-writabletype.

The optical readout device also includes a driving circuit 4 for drivingthe radiation-emitting data storage medium 2 with an applied voltagesignal which is applied across the electroluminescent layer by theelectrodes of the medium 2. One voltage is applied across the entiredata-carrying layer at any one time. The driving circuit 4 is adapted toproduce a time-varying voltage signal to produce a time-varyingradiation output from each of the data storage areas during a readcycle.

A radiation detector array 6 is adapted to detect radiation emitted froma selected area, referred to herein as a “page” P containing a pluralityof individual data storage areas, referred to hereinafter as “marks”.The detector 6 may be in the form of a complimentary metal oxide silicon(CMOS) sensor array or a charge coupled device (CCD) array.

A processing circuit 8 processes detection signals generated by theradiation detector 6 generate output data signals corresponding to thedata stored in a page currently being read from the data storage medium2, and controls operation of the drive circuit 4.

Optical system 10 is located in the optical readout device between thelocation of the data storage medium 2 and the radiation detector 6 toimage the page P currently being read out from onto the detector array.The optical system is preferably such as to resolve an area(corresponding to the area of a mark) of a size which is close to adiffraction limited spot size for the radiation emitted by the datastorage medium.

FIG. 2 illustrates brightness levels 11, 12 and 13 of the radiationoutput from three different types of mark in the data storage medium 2.Note that these are exemplary typical values, as used in one embodimentof the invention; however variation thereof will occur in dependenceupon the material used. Note that the values along the vertical axis aregiven in Candelas/m², and the values along the horizontal axis are givenin Volts.

A first type of mark, corresponding to a first data value, having amaximum emission characteristic I₁, has the highest brightness level atany selected drive voltage. A second type of mark, corresponding to asecond data value, has an intermediate emission characteristic having anintermediate brightness level I₂, at any selected drive voltage. A thirdtype of mark, corresponding to a third data value, having a lowestemission characteristic I₃ has the lowest brightness level at anyselected drive voltage. Each of the characteristics has a brightnesswhich increases with increasing levels of drive voltage. The emissioncharacteristics of the different marks, under the drive voltage asshown, increase generally exponentially in brightness with drivevoltage.

FIG. 3 illustrates elements of the drive circuit 4 and the processingcircuit 8 in one embodiment of the invention in greater detail. In thisembodiment, the drive circuit 4 includes a counting signal generatorproviding a counting signal C to a digital-to-analogue (D/A) converter22. The counting signal C is incremented periodically, at regularintervals, during a read cycle. The digital-to-analogue convertergenerates a continually-varying applied voltage signal A in accordancewith the received counting signal C, which is applied to the electrodesof the data storage medium 2. The applied signal is preferablyapproximately linearly varying.

The data storage medium 2 includes a plurality of different types ofdata storage areas. In this embodiment, there are three different typesof marks, corresponding to a three-level coding scheme. Each datastorage area corresponds to a different data value, such that threedifferent data values may be present in any particular data storagearea. The number of different data values (in this example three)possible in any particular data storage area is referred to herein asthe number of coding levels in the multi-level coding scheme. Thecounting signal generator 20 is adapted to generate a counting signalwhich varies with the frequency at least twice the number of codinglevels of the data storage medium per read cycle.

The counting signal C is also supplied to a signal processor 24 whichuses the counting signal to process detection signals from the detectorarray 6, and a sampling rate corresponding to the counting signal C. Inorder to allow for output level variations, within certain tolerances,allowed for each different mark type, the count signal preferably has afrequency at least four times that of the number of coding levels perread cycle, so that each mark type can be reliably distinguished.

The detector array 6 generates a different output signal D₁, D₂ . . .D_(n) for each pixel, or set of pixels, referred to herein as adetector, in the detector array corresponding to an area of eachdifferent mark in the page P currently being read. Each of thesedifferent detection signals is separately processed at the signalprocessor 24. The output of each detector in the detector array 6increases during a read cycle as the amount of light output from eachmark in the data storage medium 2 increases under the influence of thegradually increasing applied voltage signal A. The output from eachdetector reaches a saturation level at a certain time within the readcycle, corresponding with the mark type. Mark types which emitrelatively large amounts of radiation emit radiation in such quantitiesas to cause saturation of the corresponding detector, at an early partof the read cycle. Conversely, mark types emitting relatively smallamounts of radiation cause saturation in the corresponding detector, ata relatively late stage in the reading cycle, when the applied voltage Ahas increased sufficiently to cause saturation of the correspondingdetector.

The signal processor 24 includes threshold level sensors correspondingto each detection signal D₁, D₂ . . . D_(n), which are triggered whenthe output from the corresponding detector nears saturation. Ontriggering of the threshold level sensor, the current count of thecounting signal C is stored in latch memory 26 in a memory locationcorresponding to that of the location of the detector within detectorarray 6. The applied signal A is increased until such time as allthreshold level sensors have been triggered, at which point the signalprocessor 24 initiates a new read cycle, to read adjacent page on thedata storage medium 2.

For each read cycle, an output data signal O is read out from the latchmemory 26 to further data processing elements of the device in which thedata read out components are installed.

FIG. 4(A) to (C) illustrate detection signals corresponding to each ofthe mark types generating the brightness curves 11 to 13 respectivelyshown in FIG. 2. All of FIG. 4(A) to (C) show a time axis marked withthe points of incrementation of the count signal C, the count signal Cbeginning at zero and incrementing in discrete integral steps to fiveduring a single read cycle.

At the start of the read cycle, digital-to-analogue converter 22generates the lowest applied voltage A of the read cycle, and begins toincrease the applied voltage A linearly during the remainder of the readcycle. In this embodiment the number of coding levels is three and thefrequency of the count signal is six increments per cycle. A markcreating a saturation level at the detector within the first twocounting periods is determined to be a mark of a first type, havingmaximum electroluminescent characteristics. Correspondingly, a markcreating saturation at the detector within the third or fourth countingperiods is determined to be a mark of a second type, having intermediateelectroluminescent characteristics, whereas a mark creating saturationat the corresponding detector within the fourth or fifth countingperiods is determined to be a mark of the third type, having lowestelectroluminescent characteristics. The times at which saturation of thedetector is sensed in signal processor 24 for each of these differentmark types, t₁, t₂ and t₃ respectively, are shown in each of FIG. 4(A)to (C). The signal processor 24 detects each of these times within thecycle by means of the threshold detector and determines the data valueusing the current count in the counting signal C before writing thecorresponding data element into latch memory 26. After the reading ofthe mark in the page of lowest emissivity, the applied signal A isre-set to zero, and the output of each of the detectors returns to zerobefore the start of the next read cycle.

Note that FIG. 4(A) to (C) illustrate output signals from radiationdetector having generally linear output response characteristics. In analternative embodiment, processing circuitry is associated with eachdetector to modify the detector characteristics, for example to producea generally logarithmic output response characteristic, whereby theapproach of the saturation point become more pronounced, i.e. the outputresponse gradient near the point of saturation is increased in relationto a linear output response.

In the above-described embodiment, the driving circuit 4 includes asignal generator 22 which generates the applied signal A in accordancewith timing reference signals provided by the counting signal generator20. Furthermore, the signal processor 24 also receives the countingsignal, to synchronize processing of the detection signal D₁, D₂ . . .D_(n) with the applied signal A. In this case, the common timing sourceis in the form of a digital signal generator. In an alternativeembodiment, the applied voltage A may be generated by an analogue signalgenerator forming the common timing source. The timing may betransferred via an analogue-to-digital converter in the signalprocessor, which receives the applied voltage A and generatescorresponding digital timing reference signals therefrom. These digitaltiming reference signals are used by the signal processor 24 insynchronizing the processing of the detection signals D₁, D₂ . . . D_(n)with the applied signal A.

In a further embodiment, the processing of the detection signals, ratherthan being directly synchronized with the applied signal by use of acommon timing source, synchronizes the processing of the detectionsignals with the applied signal by recognizing a characteristic of thedetection signals. For example, the detection signals may include apredetermined signal characteristic, corresponding to a reference markin the data storage medium, indicating the start of a read cycle. Hence,timing characteristics may be detected in the detection signals receivedfrom detector array 6 in order to process the detection signals todistinguish the various different types of marks. A clock signalgenerator within the signal processor 24 may be used to provide a timestamp corresponding to the saturation of each detector, which incombination with the reference timing is used to generate acorresponding digital data value in the output signal O.

The optical system 10 used in different embodiments may take variousdifferent forms. In one embodiment, the optical system images a singlearea of the data storage medium 2 which corresponds with the pagecurrently being read. This type of optical system may be used incombination with a mechanical “step and scan” system which mechanicallymoves the data storage medium in relation to the optical system 10 toallow successive adjacent pages to be read during different read cycles.

In the above described embodiment, the data storage medium 2 includes anelectroluminescent material arranged between two uniform electrodes,such that the entire electroluminescent layer is activated irrespectiveof the location of the page P currently being read. This simplifies thecircuitry required in order to perform reading out of data from the datastorage medium 2. However, in an alternative embodiment, theelectroluminescent material is arranged between an array of addressableelectrodes, such that an area corresponding to a page currently beingread is selectively activated during each read out cycle. In thisembodiment, the optical system 10 may be arranged to image a pluralityof areas corresponding to different pages distributed across the datastorage medium 2 simultaneously on to the detector array 6, with theimage of each page area occupying the entire defective detector arrayarea This reduces the need for mechanical scanning in the device.Namely, a plurality of pages may be scanned sequentially without formingmechanical scanning. In one example of this embodiment, all of theinformation-carrying area on the medium, containing a plurality of pagesof data, is simultaneously imaged on to the detector array 6, therebyavoiding any need for mechanical scanning.

In one embodiment of the invention, the detector array 6 is in the formof a one-dimensional detector array, consisting of a plurality ofdetectors arranged in a line. In a second embodiment of the invention,the detector array 6 is in the form of a two-dimensional array ofdetectors, having a rectangular formation.

Note that, whilst in the above-described embodiments, a three-level datacoding scheme is used in the data storage medium, this is used forexemplary purposes only. Preferably, a higher number of data codinglevels are used. The multilevel coding scheme may be selected tocorrespond for example to 8, 12, 16 or 32 bit data signals being readfrom each mark. On the other hand, the invention may also be applied ina binary data coding scheme. The number of coding levels used inpractice will preferably depend on the signal-to-noise ratio in thesystem, whereby the number of coding levels chosen will be low enough toallow the different levels to be accurately resolved and otherwise ashigh as possible to increase to the data density in the recordingmedium.

The invention may be embodied in data readout devices capable of readingdifferent formats of data storage medium having different data codingschemes corresponding to different numbers of levels ofelectroluminescence. For example, one format of data storage medium mayhave three levels of electroluminescence corresponding to threedifferent data coding schemes, whilst a second format of data storagemedium may have four levels of electroluminescence corresponding to afour-level data coding scheme. In order to successfully read out datafrom each of these different formats of data storage medium, none of thecomponents of the device need to be replaced. Rather, the signalprocessor 24 may operate in two different processing modes,corresponding to each different data storage medium format to beaccommodated. Furthermore, the frequency of the timing reference signalmay be varied in the different modes. For example, in the embodimentillustrated in FIG. 3, the count signal C may be increased, relative tothe counting frequency when reading the three-level medium, when readingthe four-level medium.

In the above embodiments, the light-emitting material is preferably anorganic material such as one of, or a combination of, a number of knownelectroluminescent polymers. Examples include polypyridines,polypyridyvinylenes, polyphenylenes, polyphenylenevinylenes,polythiophenes, polyvinylcarbazoles, polyfluorenes,polynaphthalenevinylenes, polyphenyleneacetylenes,polyphenylenediacetylenes, polycyanoterephthalylidenes,polyphenylenebenzobisthiazoles, polybenzimidazobenzophenanthrolines,polypyridine copolymers, polypyridylvinylene copolymers, polyphenylenecopolymers, polyphenylenevinylene copolymers, polythiophene copolymers,polyvinylcarbazole copolymers, polyfluorene copolymers,polynaphthalenevinylene copolymers, polyphenyleneacetylene copolymers,polyphenylenediacetylene copolymers, polycyano-therephthalylidenecopolymers, polyphenylenebenzobisthiazole copolymers andpolybenzimidazobenzophenanthroline copolymers.

Whilst in the above embodiments a single electroluminescent layer isdescribed, the invention is also applicable to multi-layer mediums. Inthe case of read out from multi-layer mediums, the layers areselectively activated during read out.

The above embodiments are to be understood as illustrative examples ofthe invention. Further embodiments of the invention are envisaged. Forexample, instead of reading a data medium by electroluminescence, it isalso possible to utilize the invention in relation to a fluorescent datastorage and readout system. In this case, the data storage mediumincludes a layer of fluorescent material which is activated under theinfluence of an applied UV radiation signal which has the sametime-varying characteristics as described above in relation to theapplied voltage signal A. In this manner, readout from a multi-levelcoded fluorescent data storage medium is provided by use of theinvention.

It is to be understood that any feature described in relation to oneembodiment may also be used in other of the embodiments. Furthermore,equivalents and modifications not described above may also be employedwithout departing from the scope of the invention, which is defined inthe accompanying claims.

1. An optical readout device for reading out data from aradiation-emitting data storage medium, said medium comprising aradiation-emitting material holding data in the form of data storageareas capable of emitting varying amounts of radiation on application ofan applied signal, said data storage areas including at least a firsttype of data storage area and a second type of data storage areaindicating different first and second data values, said devicecomprising: a driving part for driving the radiation-emitting materialwith an applied signal; a radiation detecting part for detectingradiation emitted from said data storage areas and for generatingradiation detection signals; and a processing part for processing saiddetection signals to generate data signals corresponding to the datastored in the medium; wherein said driving part is arranged to generatea time-varying applied signal, and wherein the processing part isarranged to process the detection signals to distinguish a detectionsignal resulting from reading said first type of data storage area froma detection signal resulting from reading said second type of datastorage area in dependence on a temporal characteristic of the detectionsignals.
 2. An optical readout device according to claim 1, wherein saiddriving part is adapted to generate a substantially continually varyingapplied signal.
 3. An optical readout device according to claim 2,wherein said applied signal is approximately linear.
 4. An opticalreadout device according to claim 1, wherein said driving part and saidprocessing part are connected to a common timing source whereby theprocessing of the detection signals is synchronized with the appliedsignal.
 5. An optical readout device according to claim 4, wherein saidcommon timing source is a digital signal generator.
 6. An opticalreadout device according to claim 5, comprising a digital-to-analogueconverter for generating the applied signal.
 7. An optical readoutdevice according to claim 4, wherein said common timing source is ananalogue signal generator.
 8. An optical readout device according toclaim 7, wherein said analogue signal generator is used to generate theapplied signal.
 9. An optical readout device according to claim 7,comprising an analogue-to-digital converter for generating a digitaltiming signal.
 10. An optical readout device according to claim 1,wherein said processing part is adapted to synchronize the processing ofthe detection signals with the applied signal by recognizing acharacteristic of the detection signals.
 11. An optical readout deviceaccording to claim 1, wherein the device is adapted for the readout ofdata from a data storage medium comprising a radiation-emitting materialholding data in the form of data storage areas at least a first type ofdata storage area, a second type of data storage area and a third typeof data storage area.
 12. An optical readout device according to claim11, wherein said processing part is adapted to distinguish a detectionsignal resulting from reading said third type of data storage area fromdetection signals resulting from reading said first and second type ofdata storage area in dependence on a temporal characteristic of thedetection signals.
 13. An optical readout device according to claim 11,wherein the device is adapted for the readout of data from a first datastorage medium, comprising a radiation-emitting material holding data inthe form of a first plurality of different types of data storage area,and from a second data storage medium comprising a radiation-emittingmaterial holding data in the form of a second plurality of differenttypes of data storage area, the number of different types of datastorage areas in said first and second medium being different.
 14. Anoptical readout device according to claim 13, wherein said processingpart is adapted to alter the processing of the detection signals independence upon whether data is being read out from a said first datastorage medium or a said second data storage medium.
 15. An opticalreadout device according to claim 1, wherein said radiation detectingpart comprises a one-dimensional array of radiation detectors.
 16. Anoptical readout device according to claim 1, wherein said radiationdetecting part comprises a two-dimensional array of radiation detectors.17. An optical readout device according to claim 1, wherein saidradiation emitting material comprises an electroluminescent material andwherein said applied signal is a voltage signal.
 18. An optical readoutdevice according to claim 1, wherein said radiation emitting materialcomprises a fluorescent material and wherein said applied signal is aradiation signal.